1. Field of the Invention
The invention relates to a method and an apparatus for detecting a particular material in an object, particularly in a piece of luggage, by means of electromagnetic radiation, in which the intensities of unabsorbed radiation from at least three radiation planes are measured and evaluated in associated detector devices.
2. Description of the Background Art
Methods and apparatus for the inspection of objects are used, in which the object is conveyed through electromagnetic radiation, emitted by stationary radiation sources, as is well-known, for example, for security inspection of pieces of luggage at airports. The intensities of the unabsorbed radiation are measured and evaluated by the likewise stationary detector devices assigned to the radiation sources. Typically, the inspection occurs with use of x-rays.
A method is disclosed in WO 03/031960, which corresponds to U.S. Pat. No. 7,020,241, and which is incorporated herein by reference, and in which five stationary radiation sources emit x-rays in radiation planes, three of which run parallel to one another and perpendicular to the transport direction of the objects through the luggage inspection device. It is verified according to the following method from the data of the detector devices associated with the radiation sources whether a suspected material is also actually present:
First, a two-dimensional image of the object is produced and then an area shown on the image based on the value of a material variable is selected for checking; an absorption thickness of the area is then determined with use of a stored value, and concurrently the corresponding thickness of the area is determined from spatial position data, which were determined solely from the measured intensity values. It is then determined by a comparison of the two determined values whether the suspected material is in fact present. In the method, the intensities of two energy ranges are evaluated separately in a known manner in the so-called dual-energy method, x-rays being evaluated in energy ranges below (low range) and above (high range) about 70 keV.
This advantageous method works differently from known computer tomographs with a low number of less than 10 views, which are produced with a suitable number of stationary radiation sources and stationary detectors. A complex object cannot be fully reconstructed for mathematical reasons with this low number of views. Therefore, this method is restricted to the obtainment of partial information from particular regions, which are selected from single views and checked further.